Overheat and smog fail

[Ecomike]

I've had good luck using small paper clips for back probing and alligator clips.

Good suggestion.


His problem may be the location of the O2 sensor harness connector on Renix. It is hard to reach. I added a second set of one pin connectors to mine near the throttle body, The O2 sensor connector wire on the sensor is too short to get easy access.

 

[88trailcrawler]

I can't find an analog volt meter in town to save my life, checked auto parts stors, sears, electronic supply, radio shack, etc. Everything is digital the closest thing I found was $5.00 bargin bin one, I figured was not going to be High Empendance.

So....

Pretty sure the O2 sensor that was installed during emmissions tests was the one that tested bad at the heater element.

I put in the back up O2 sensor and rigged up a good test contact point. Drove the jeep around to get everything up to temp.

With only a digital MM available:
- Confirmed 5v signal with key on

- At idle the numbers are jumping, readings appear to be in the 1v-4v range with an occasional .88v or 4.5v. (again the numbers are jumping around)

- At 2000rpm (best I can tell not seeing the tach) the numbers are STILL jumping around. (Definatley not a steady voltage) Readings are higher in the 2.5v - 5.5v range with occassional 1.88v and maybe 5.88v readings.

Still testing an OLD O2 sensor.

Question NOW is:
- Is the varied reading at RPM enough to indicate a bad sensor?

 

[Pelican]

Walmart has one for $11 locally. Note that this is a "professional quality" meter! Yeah, sure... but would probably do for your immediate purposes.

 

[crash02]

On renix the voltage range you are getting is showing the sensor is working. I used a harbor freight cheapy digital meter and got the same numbers you are getting, after I found out my relay for the heater element was grounded in the open position. P.o. Had a wire from the relay pole to ground, not sure what they were trying to do.
not sure if my ramblings help, but you are on the right track for sure.

 

[Ecomike]

You can not get 5.5 volts if the input is only 5.0 volts, so that is odd data for sure, may just be the junping around issue of the display.

But 2.5 to 5.0 is a problem. May be the sensor, may be something else. Check the input voltage again (from the ECU), warmed up at various speeds (in park) It should be stable at 4.7 to 5.1 V!

Check the fuel pressure at higher RPMs too.

2.5 V to 5 V is lean, so the O2 sensor is telling the ECU the engine is lean, and the ECU adds fuel as much as it can (making it rich!!!!). If the reading stays lean (2.5 to 5) then you must have an intake manifold leak (which usually causes a high idle!!!!), or an exhaust manifold leak confusing the O2 sensor!!! Like a donut leak, or a cracked exh manifold, or exh manifold gasket leak (both are common!!!!!).

I can't find an analog volt meter in town to save my life, checked auto parts stors, sears, electronic supply, radio shack, etc. Everything is digital the closest thing I found was $5.00 bargin bin one, I figured was not going to be High Empendance.

So....

Pretty sure the O2 sensor that was installed during emmissions tests was the one that tested bad at the heater element.

I put in the back up O2 sensor and rigged up a good test contact point. Drove the jeep around to get everything up to temp.

With only a digital MM available:
- Confirmed 5v signal with key on

- At idle the numbers are jumping, readings appear to be in the 1v-4v range with an occasional .88v or 4.5v. (again the numbers are jumping around)

- At 2000rpm (best I can tell not seeing the tach) the numbers are STILL jumping around. (Definatley not a steady voltage) Readings are higher in the 2.5v - 5.5v range with occassional 1.88v and maybe 5.88v readings.

Still testing an OLD O2 sensor.

Question NOW is:
- Is the varied reading at RPM enough to indicate a bad sensor?

 

[Ecomike]

Cheap analog meter may work on the Renix, but won't work on the HO, 91+ O2 sensors.

 

[Ecomike]

What does the meter read during rapid acceleration and deceleration in Park?

 

[crash02]

I thought the renix o2 ranges jump from .8-4.8 volts and for the ho
.1-.9 volts? I do know there is a differences between ho and renix(smog tech explained it to me once),I chased a rich condition for a long time but that was almost 4 years ago and don't remember exactly, other then the voltage should be jumping from high to low.

 

[88trailcrawler]

First of all testing these things is a pain. I ended up clipping a length of wire to the sensor signal wire a pulled it up to the top of the engine so I could test from above. Pulling and installing HOT sensors is not fun.

I got curious and decided to compare the two sensors I have.

The sensor that was installed during the smog tests was jumping noticably slower and a narrower range and actually stuck at 5v with the engine running.

My (hopeful) theroy is that sensor #1 (installed at time of smog tests) was "bad" based on no resistance detected on the heater element side of the sensor and "Lazy" based on the noticably slower voltage jump, narrower range and holding at steady 5v with engine running.

My other (hopeful) optimistic theroy is that Sensor #2 (not yet smog tested) will produce a different result based on testing somewhat near the desired range (as best as I can tell with the jumping digital MM) and the fact that the resistance at the heater side of the sensor was within the desired range.

And my final (hopeful) optimistic theroy is that the overheating condition exacerbated my CCV, Doughnut, manifold, valve cover, etc. issues that further contributed to my emissions problem.

Is any of this logical or just hopeful? (Fingers crossed)

Hoping to re-smog tomorrow, waiting for some thoughts.

 

[Ecomike]

This statement (bold part) does not make sense?

My (hopeful) theroy is that sensor #1 (installed at time of smog tests) was "bad" based on no resistance detected on the heater element side of the sensor and "Lazy" based on the noticably slower voltage jump, narrower range and holding at steady 5v with engine running.

Can't be steady at 5V and have a range? Was this ALL with the engine running, or sometimes the engine running.

Sorry to be so picky, but I work in world were statements of data need to be precise, as lives depend on it...

So far the early data tells me it is still running rich with sensor #2, because the O2 sensor is sending a lean reading of 2.5 to 5.5?

Look for cracks at the welds on the exh manifold. Check all the manifold bolts for loose ones, top and bottom. At idle shoot some carb cleaner in the intake, to see if pegs the meter at =<1.0 V.

 

[88trailcrawler]

Sensor 1 was bouncing slower and in a narrower range than sensor 2 and then locked in at 5v with the engine running. Anyway, with the that and the heater element fail, I have trashed sensor 1.

I'll go grab that cheapie tester and see if I can get more reliable data.

I did find a loose manifold bolt and leak early on in this (way too long) saga. I was fairly certain all was good (intake/exhaust) but I will recheck and try to get a snug up wrench on the lower bolts.

This is difficult because the jeep is running good. I can't just fire it up and "see if that works" like a typical driveway mechanic. My only test is the smog test.

Thanks for all the help so far, I'll report back once I get solid test data.

 

[Ecomike]

All vehicles run good when run a little rich, till the Cat chokes, LOL.

When you get it right, it will run between 2-3 volts at a steady (about 2000) rpm, and about 1-4 volts at idle.

I doubt you have one, but intake leaks can be found spraying carb cleaner around the intake manifold and the throttle body gaskets. It is possible to have a nested intake-exhaust leak close to each other, with one feeding the other, the way they share bolts and the same gasket so close!!

And sensor 2 may be good!!!! So lets stay focused on the analog meter test next!

 

[88trailcrawler]

See below

 

[88trailcrawler]

Disregard previous post, I am an idiot and mis read the multi meter scale. (Don't judge me)

HERE IS CORRECT DATA:
- Key on, engine off: 5v

- Idle: 1.5/2.0v to 3.5/4.5v - Looks about right?

- Approx. 2,000rpm: 2/2.5v to 3.5v -Looks about right?

- Rapid throttle pump: .5v to 1v (rapid pump, not really letting RPM's drop) -Pumping Gas in, seems right?

- Controlled accel/Decel: 1v to 5v. (Throttle up 1v, release and let RPM's drop 5v, Throttle up 1v) - Pumping gas in, volts drop, sucking air in volts raise - Seems about right?

- Idle as above, with a short blast of carb cleaner in the intake tube it drops to <1v - Spraying fuel in voltage drops - Seems right?

What's next?

Keep in mind this is NOT the sensor that I smog tested with....I suppose I could run the same test with the sensor that failed, see if was causing the problem.

 

[Ecomike]

That all looks excellent so go run the smog test, before the jeep gremlins come back out of hibernation!!!!

:cheers:

Disregard previous post, I am an idiot and mis read the multi meter scale. (Don't judge me)

HERE IS CORRECT DATA:
- Key on, engine off: 5v

- Idle: 1.5/2.0v to 3.5/4.5v - Looks about right?

- Approx. 2,000rpm: 2/2.5v to 3.5v -Looks about right?

- Rapid throttle pump: .5v to 1v (rapid pump, not really letting RPM's drop) -Pumping Gas in, seems right?

- Controlled accel/Decel: 1v to 5v. (Throttle up 1v, release and let RPM's drop 5v, Throttle up 1v) - Pumping gas in, volts drop, sucking air in volts raise - Seems about right?

- Idle as above, with a short blast of carb cleaner in the intake tube it drops to <1v - Spraying fuel in voltage drops - Seems right?

What's next?

Keep in mind this is NOT the sensor that I smog tested with....I suppose I could run the same test with the sensor that failed, see if was causing the problem.

 

[88trailcrawler]

Seonsor 1 tested (The one that failed smog)

Comparison:
AT IDLE:
#1: 2.5v - 3v (inconsistant with occasional jump 2v - 4v)
#2: 1.5v -3.5v (occasional swing of 2v - 2.5v)

NOTE: #1 stuck at 5v at start of test, seemed slower and less consistant. Also, note that #1 is NOT getting below 2.5 at idle.

AT 2,000 RPM:
#1 2.25v - 3.75v
#2 2.0/2.5v - 3.5v

THROTTLE PUMPING:
#1 2.5v
#2 .5v - 1.0v

RPM UP/DOWN:
#1 1.5v - 5v
#2 1.0v - 5v

AT IDLE (with quick spray of carb cleaner)
#1 1.5v
#2 <1.0v

NOTE: That sensor 1 would not peg below 1.0 even when spraying enough in to hesitate engine.

SENSORS:
I would like to know if you think sensor #1 was a likely factor in the Smog fail? Have a found and fixed something since last fail?

I do think #1 has some issues. It has now pegged at 5v with the engine running during two different test days. It does not appear to be reacting consistantly or as quickly as #2 and it is the one that tested bad on the heater element.

Hard data is difficult with the needle bouncing, engine running, etc and there may be variables due to temps, RPM's, Etc. But it does appear that sensor #1 (the failed sensor) is not dropping into the lower voltage range same as #2. I assume low voltage = less fuel?

How I would love to hear that Sensor #1 (the failed sensor) is bad, but I just don't know if the numbers show that.


MANIFOLDS:
Remember that I did find a top/front leak using starter fluid after the first test, I used a bit of RTV and tightened a loose bolt. Still missing the front lower exhaust manifold bolt.

Crawled underneath today, could only get a wrench on two lower bolts, both were tight (well at least not loose)

Lower rear exhaust stud has no nut on it! It's oily right below on the block but I don't know if that is from my valve cover leak (Engine bay was a mess at the start of this)

Anyway, started engine and unloaded starter fluid, carb cleaner, etc around the top and bottom of the manifold gasket areas and didn't find any change in idle. Really focused on area of missing bolt, no change in idle.

Bottom line is the that the manifolds could be suspect, and probably warrant some attention one day, I don't know if they are contributing to the smog failure. - Just ran out there again with help, had my kid hold the jeep at about 2,000rpm's and unloaded starter fluid and carb cleaner again at RPM top and bottom of manifold gasket area and got no change.

Then stuck MM on sensor #1 (failed sensor) that is still installed. and got very little meter movement, like 2.5v - 3v at idle and a bit lower at RPM.

So........what do you think now? :worship: Go test with Sensor #2?

 

[Ecomike]

Sensor#1 IS BAD!!!! Use sensor #2!!!

That all looks excellent so go run the smog test, before the jeep gremlins come back out of hibernation!!!!

:cheers:

 

[88trailcrawler]

arty:arty:arty:arty:
PASSED:
Test = 15mh/25mph

CO = 14.3/14.3
O2 = 0.7/0.6
HC = 0/1
CO = 0.00/0.02
NO = 0/0

New test guy clearly wanted it to pass, old test guy seemed more like smog police. New test was much shorter, in a much larger test bay and the guy set a huge fan in front of the jeep

What I have learned:
- Naxja is invaluable (must renew my membership a.s.a.p.)
- Ecomike is awesome
- My jeep is old
- Not all smog test places are the same.
- A lot of stuff about my jeep I never new before
- My jeep is actally in pretty good shape
- There is still a TON of stuff my jeep needs

Now this thread MUST DIE!

Thanks to everyone who pitched in.

 

[crash02]

Sweet! and congratulations!

 

[Ecomike]

I never doubted it would!!!!!

:cheers:

arty:arty:arty:arty:
PASSED:
Test = 15mh/25mph

CO = 14.3/14.3
O2 = 0.7/0.6
HC = 0/1
CO = 0.00/0.02
NO = 0/0

New test guy clearly wanted it to pass, old test guy seemed more like smog police. New test was much shorter, in a much larger test bay and the guy set a huge fan in front of the jeep

What I have learned:
- Naxja is invaluable (must renew my membership a.s.a.p.)
- Ecomike is awesome
- My jeep is old
- Not all smog test places are the same.
- A lot of stuff about my jeep I never new before
- My jeep is actally in pretty good shape
- There is still a TON of stuff my jeep needs

Now this thread MUST DIE!

Thanks to everyone who pitched in.